113 km ESE of Chignik, Alaska

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 39 km (24 mi) from the epicentre. Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

How big was it?

This earthquake released about 1,900 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 180,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 7,900× the energy of this one
3. Magna, Utah 2020 M 5.7 5,600× the energy of this one
4. This earthquake M 3.2 about 1,900 lb of TNT
5. Around the size people start to feel M 3.0 this one released 2× more

Energy from the Gutenberg–Richter relation (log₁₀E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 6.9 on 2021-10-11 — about 350,000 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 113 km ESE of Chignik, Alaska · 25 km SSW of this epicentre May 4, 1923
2. 6.9 143 km ESE of Chignik, Alaska · 35 km SE of this epicentre Feb 13, 1951
3. 6.6 128 km SE of Chignik, Alaska · 48 km S of this epicentre Jul 28, 1934
4. 6.4 77 km ESE of Chignik, Alaska · 36 km WNW of this epicentre Mar 24, 1972
5. 6.3 112 km E of Chignik, Alaska · 15 km N of this epicentre Feb 25, 1953

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 56.0508, -156.6324. Map © OpenStreetMap contributors.

Aftershocks so far

58 earthquakes have been recorded within 50 km since this one.

1. 2.4 Alaska Peninsula 06:33 UTC
2. 2.1 115 km E of Chignik, Alaska 19:52 UTC
3. 1.6 Alaska Peninsula 18:22 UTC
4. 1.8 111 km E of Chignik, Alaska 19:05 UTC
5. 1.8 Alaska Peninsula 22:06 UTC
6. 2.8 114 km E of Chignik, Alaska 14:37 UTC
7. 2.2 101 km E of Chignik, Alaska 08:45 UTC
8. 2.5 105 km E of Chignik, Alaska 06:31 UTC
9. 2.6 114 km E of Chignik, Alaska 01:15 UTC
10. 3.6 107 km E of Chignik, Alaska 02:41 UTC
11. 2.2 99 km E of Chignik, Alaska 00:52 UTC
12. 2.2 116 km E of Chignik, Alaska 12:15 UTC
13. 1.8 127 km E of Chignik, Alaska 17:48 UTC
14. 2.4 114 km E of Chignik, Alaska 14:11 UTC
15. 3.1 124 km E of Chignik, Alaska 20:16 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:23 UTC. QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

• The official USGS event page — the source of record for every value above
• Did you feel it? Report it to USGS — reports go to USGS, not to us
• ShakeMap for this event, when USGS has produced one

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.